Communication device and communication method

ABSTRACT

According to a communication method of the present disclosure, a responder, after the end of transmission sector sweep (TXSS), receives from an initiator a first feedback frame including a BF training type FIELD indicating whether or not to implement a beam forming training (BFT) of a single user multi-input multi-output (SU-MIMO). If the BF training type FIELD indicates that a BFT of the SU-MIMO is to be implemented, the responder transmits to the initiator a second feedback frame based on the result of the TXSS and including a signal to noise ratio (SNR) and a sector identifier (ID) order. The initiator implements the BFT of the SU-MIMO between the initiator and the responder on the basis of the SNR and the sector ID order.

TECHNICAL FIELD

The present disclosure relates to a communication apparatus and acommunication method.

BACKGROUND ART

The IEEE802.11ay standard (referred to as “11ay standard”) has beendeveloped as a system for achieving high-speed data transmission byapplying a MIMO system to millimeter-wave communication (see Non-PatentLiteratures (hereinafter, referred to as “NPLs”) 2, 3, and 4).

CITATION LIST

Non-Patent Literature

NPL 1

IEEE802.11ad-2012

NPL 2

IEEE802.11-17/1233r1

NPL 3

IEEE802.11-18/0430r2

NPL 4

IEEE802.11-18/0089r0

SUMMARY OF INVENTION

There is a need to shorten the time taken to perform beamformingtraining (BFT) according to the 802.11ad standard (see PTL 1).

In a communication method according to one aspect of the presentdisclosure, an initiator transmits a first feedback frame to aresponder, the first feedback frame including a BF training type FIELDindicating whether or not beamforming training (BFT) for Single UserMulti-Input Multi-Output (SU-MIMO) is performed after transmissionsector sweep (TXSS) ends; the responder receives the first feedbackframe, and transmits second feedback frame to the initiator when the BFtraining type FIELD indicates that the BFT for SU-MIMO is performed, thesecond feedback frame including a Signal to Noise Ratio (SNR) and asector Identifier (ID) order based on a result of the TXSS; and theinitiator receives the second feedback frame, and performs the BFT forSU-MIMO between the initiator and the responder based on the SNR and thesector ID order.

In a communication method for an initiator according to one aspect ofthe present disclosure, the method including: transmitting a feedbackframe to a responder, the feedback frame including a BF training typeFIELD indicating whether or not BFT for SU-MIMO is performed after TXSSends; and when second feedback frame including an SNR and a sector IDorder based on a result of the TXSS is received from the responder,performing the BFT for SU-MIMO between the initiator and the responderbased on the SNR and the sector ID order.

In a communication method for a responder according to one aspect of thepresent disclosure, the method including: receiving a first feedbackframe from an initiator, the first feedback frame including a BFtraining type FIELD indicating whether or not beamforming training (BFT)for Single User Multi-Input Multi-Output (SU-MIMO) is performed aftertransmission sector sweep (TXSS) ends; transmitting second feedbackframe to the initiator when the BF training type FIELD indicates thatthe BFT for SU-MIMO is performed, the second feedback frame including aSignal to Noise Ratio (SNR) and a sector Identifier (ID) order based ona result of the TXSS; and performing the BFT for SU-MIMO between theinitiator and the responder based on the SNR and the sector ID order.

It should be noted that general or specific embodiments may beimplemented as a system, a method, an integrated circuit, a computerprogram, a storage medium, or any selective combination thereof.

Additional benefits and advantages of the disclosed embodiments willbecome apparent from the specification and drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the specification and drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

The foregoing and other features of the present disclosure will becomemore fully apparent from the following description and appended claims,taken in conjunction with the accompanying drawings. With theunderstanding that these drawings only depict several embodimentsaccording to the present disclosure and are therefore should not beconsidered as limiting the scope of the present disclosure, thedisclosure is described more specifically and in more detail using theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an exemplary configuration of a MIMO communicationsystem according to Embodiment 1;

FIG. 2A illustrates an exemplary configuration of a communicationapparatus;

FIG. 2B illustrates an exemplary configuration of the communicationapparatus;

FIG. 3 illustrates an example of a BFT procedure according to the802.11ad standard;

FIG. 4 illustrates a SISO BRP TXSS procedure according to the draft802.11ay standard;

FIG. 5 illustrates an example of a SU-MIMO BFT procedure according tothe draft 802.11ay standard;

FIG. 6 illustrates an example of the SU-MIMO BFT procedure according tothe draft 802.11ay standard;

FIG. 7 illustrates an example of a MU-MIMO BFT procedure according tothe draft 802.11ay standard;

FIG. 8 illustrates an example of the MU-MIMO BFT procedure according tothe draft 802.11ay standard;

FIG. 9 illustrates a format of a BRP frame used in FIGS. 3 to 8;

FIG. 10A illustrates a format of the BRP frame to be transmitted firstwhen the communication apparatus performs the BFT procedure of FIG. 3,4, 5, 6, 7, or 8;

FIG. 10B illustrates a format of the BRP frame to be transmitted firstwhen the communication apparatus performs the BFT procedure of FIG. 3,4, 5, 6, 7, or 8;

FIG. 10C illustrates a format of the BRP frame to be transmitted firstwhen the communication apparatus performs the BFT procedure of FIG. 3,4, 5, 6, 7, or 8;

FIG. 10D illustrates a format of the BRP frame to be transmitted firstwhen the communication apparatus performs the BFT procedure of FIG. 3,4, 5, 6, 7, or 8;

FIG. 11 illustrates a format of the BRP frame to be transmitted firstwhen the communication apparatus performs the BFT procedure of FIG. 3,4, 5, 6, 7, or 8;

FIG. 12 is a flowchart illustrating a procedure for distinguishing thetype of the BFT procedure (FIG. 3, 4, 5, 6, 7, or 8) when a responderreceives a BRP frame;

FIG. 13 illustrates the types of SISO BFT that can be used incombination with a SISO Feedback procedure of SU-MIMO BFT by aninitiator using the BRP frame of FIG. 10A, 10B, 10C, 10D, or 11 as aleading BRP frame of the procedure;

FIG. 14 illustrates details of a procedure for communication apparatusesto perform SU-MIMO BFT of FIG. 6 using the BRP frame illustrated in FIG.10A, 10B, 10C, 10D or 11;

FIG. 15 illustrates a format of a common Feedback BRP frame;

FIG. 16 illustrates a format of a BRP frame of Embodiment 2;

FIG. 17 illustrates a procedure for the initiator and the responder toperform SISO BRP TXSS and SU-MIMO BFT using the BRP frame of FIG. 16;

FIG. 18 is a flowchart illustrating a procedure for distinguishing thetype of the BFT procedure (FIG. 3, 4, 5, 6, 7, or 8) when the responderreceives the BRP frame of FIG. 16;

FIG. 19 illustrates an example of a format of the BRP frame other thanthat illustrated in FIG. 16:

FIG. 20 is a flowchart illustrating a procedure for distinguishing thetype of the BFT procedure (FIG. 3, 4, 5, 6, 7, or 8) when the responderreceives the BRP frame of FIG. 19;

FIG. 21 illustrates an example of a procedure for the initiator and theresponder to perform SISO BFT and SU-MIMO BFT;

FIG. 22 illustrates an example of the procedure for the initiator andthe responder to perform SISO BFT and SU-MIMO BFT;

FIG. 23 illustrates an example of the procedure for the initiator andthe responder to perform SISO BFT and SU-MIMO BFT; and

FIG. 24 illustrates a format of the BRP frame.

DESCRIPTION OF EMBODIMENTS

In the following detailed description, reference is made to theaccompanying drawings, which are incorporated in the description. In thedrawings, like numerals generally identify like components, unlesscontext dictates otherwise. It is readily understood that aspects of thepresent disclosure can be arranged, replaced, mixed, and designed in awide variety of different configurations, all of which are explicitlyexpected and form a part of the present disclosure.

A beamforming training (BFT) procedure according to the 802.11adstandard (see NPL 1) will be described with reference to the drawings.

FIG. 1 illustrates an exemplary configuration of a MIMO communicationsystem according to the present embodiment. Communication apparatus 100,communication apparatus 200, and communication apparatus 300 include oneor more antenna arrays. Each of the antenna arrays includes one or moreantenna elements.

Communication apparatus 100 includes two antenna arrays 101 a and 101 b,for example, and performs Single Input Single Output (SISO)communication with communication apparatus 200 and communicationapparatus 300 by using one of the antenna arrays (e.g., antenna array101 a).

Communication apparatus 100 also performs Single User Multi-InputMulti-Output (SU-MIMO) communication with communication apparatus 200and communication apparatus 300 by using a plurality of antenna arrays(e.g., antenna arrays 101 a and 101 b).

Communication apparatus 100 also performs Multi User-MIMO (MU-MIMO)communication with communication apparatus 200 and communicationapparatus 300 using a plurality of antenna arrays (e.g., antenna arrays101 a and 101 b). The communication apparatus communicates with onecommunication apparatus (e.g., one of communication apparatus 200 andcommunication apparatus 300) at the same time point (one transmissionframe) in SU-MIMO, whereas the communication apparatus communicates witha plurality of communication apparatuses (e.g., both of communicationapparatus 200 and communication apparatus 300) in MU-MIMO.

FIG. 2A illustrates an exemplary configuration of communicationapparatus 100. Communication apparatus 100 includes, by way of example,host 130, MAC circuit 120, PHY circuit 110, and RF module circuit 109.

RF module circuit 109 includes, for example, antenna arrays 101 a and101 b, switch circuits (SWs) 102 a and 102 b, transmission RadioFrequency (RF) circuits 103 a and 103 b, and reception RF circuits 104 aand 104 b. Note that, transmission Radio Frequency (RF) circuits 103 aand 103 b and reception RF circuits 104 a and 104 b may also be referredto as “transmission high-frequency circuits” and “receptionhigh-frequency circuits.”

Antenna arrays 101 a and 101 b transmit and receive radio signals.Switch circuits 102 a and 102 b are circuits for switching connectiontargets to which antenna arrays 101 a and 101 b are connected, andconnecting the antenna arrays to transmission RF circuits 103 a and 103b in a transmission operation mode or to reception RF circuits 104 a and104 b in a reception operation mode, so as to allow antenna arrays 101 aand 101 b to perform transmission and reception.

Communication apparatus 100 may also include transmission antenna arrays(e.g., transmission antenna arrays 101 a-1 and 101 a-2 (notillustrated)) and reception antenna arrays (e.g., reception antennaarrays 102 a-1 and 102 a-2 (not illustrated)) instead of switch circuits102 a and 102 b.

Transmission RF circuits 103 a and 103 b modulate transmission basebandsignals output by D/A converters 111 a and 111 b, convert thetransmission baseband signals into high-frequency signals (e.g., 60 GHzband signals), and output the high-frequency signals to antenna arrays101 a and 101 b. In addition, transmission RF circuits 103 a and 103 bcontrol the phase and/or output of output signals for each of theantenna elements (not illustrated) constituting antenna arrays 101 a and101 b, thereby performing a transmission directivity control for antennaarrays 101 a and 101 b. Note that the transmission directivity controlis to control the transmission strength of a radio signal depending on atransmission direction.

Reception RF circuits 104 a and 104 b convert reception radio signalsoutput from antenna arrays 101 a and 101 b into reception basebandsignals, and output them to A/D converters 112 a and 112 b. Reception RFcircuits 104 a and 104 b control the phase and/or output of inputsignals for each of the antenna elements (not illustrated) constitutingantenna arrays 101 a and 101 b, thereby performing a receptiondirectivity control for antenna arrays 101 a and 101 b. Note that, thereception directivity control is to control the reception sensitivity ofa radio signal depending on a reception direction.

PHY circuit 110 includes, by way of example, D/A converters 111 a and111 b, A/D converters 112 a and 112 b, coding and modulation circuit114, and demodulation and decoding circuit 115.

D/A converters 111 a and 111 b perform digital/analog conversion on atransmission digital baseband signal output from coding and modulationcircuit 114, and output it to transmission RF circuits 103 a and/or 103b.

A/D converters 112 a and 112 b perform analog/digital conversion on areception analog baseband signal output from reception RF circuits 104 aand/or 104 b, and output the converted signal to demodulation anddecoding circuit 115.

Array control circuit 113 instructs, based on an instruction from BFcontrol circuit 124 of MAC circuit 120, transmission RF circuits 103 aand/or 103 b or reception RF circuits 104 a and/or 104 b to perform thetransmission directivity control or the reception directivity control.

Coding and modulation circuit 114 encodes (e.g., Low Density ParityCheck (LDPC) coding) and modulates (e.g., π/2-Binary Phase Shift Keying(BPSK)) a transmission MAC frame (referred to as “transmission PHYpayload”) output from frame generation circuit 122 of MAC circuit 120,so as to generate the transmission digital baseband signal and outputthe signal to D/A converter 111 a or 111 b.

Demodulation and decoding circuit 115 demodulates and decodes areception digital baseband signal output from A/D converters 112 aand/or 112 b, and outputs decoded PHY data (referred to as “receptionMAC frame”) to frame reception circuit 123 of MAC circuit 120.

The demodulation processing performed by demodulation and decodingcircuit 115 includes, for example, synchronization processing (preambledetection, frequency synchronization, and/or timing synchronization),equalization (correction of distortion of a reception signal), and datademodulation (e.g., conversion of π/2-BPSK symbol data into bit data andlikelihood data). In addition, the decoding processing includes, forexample, LDPC decoding.

MAC circuit 120 includes, by way of example, access control circuit 121,frame generation circuit 122, frame reception circuit 123, andbeamforming (BF) control circuit 124.

Access control circuit 121 switches between the transmission mode andthe reception mode and determines a transmission timing depending onuser data input from host 130 and received data, and controls framegeneration circuit 122, frame reception circuit 123, and/or BF controlcircuit 124. The access control circuit also determines the transmissiontiming and controls frame generation circuit 122 in order to transmitthe user data input from host 130. Further, the access control circuitdetermines a BFT execution timing and controls BF control circuit 124 inorder to perform the beamforming training (BFT).

Host 130 includes, for example, a Central Processing Unit (CPU) or aSystem on Chip (SoC) and operates an Operating System (OS) orapplication software (e.g., a web browser or file management software).The host starts or stops the MAC circuit, controls obtainment of statusinformation of the MAC circuit, requests data transmission from the MACcircuit, and/or obtains reception data, for example, in response to arequest of the OS or application software.

FIG. 2B illustrates an exemplary configuration of communicationapparatus 100 a. Another example different from communication apparatus100 is illustrated. Communication apparatus 100 a includes, for example,host 130, MAC circuit 120, PHY circuit 110 a, and RF module circuit 109a.

PHY circuit 110 a includes Intermediate Frequency (IF) transfer circuit152. IF transfer circuit 152 modulates an analog baseband signal(referred to as “IQ signal”) output from D/A converters 111 a and/or 111b into what is called a transmission Intermediate Frequency (IF) bandsignal with an intermediate frequency between the frequency of atransmission baseband signal and the frequency of an RF signal, andtransfers the modulated signal to the RF module circuit via IF cable153. Further, IF transfer circuit 152 may modulate a control signaloutput from array control circuit 113 into an IF band control signal,multiplex the modulated signal with the transmission IF band signal, andoutput the resultant signal to IF cable 153.

RF module circuit 109 a includes IF transfer circuit 151. The RF modulecircuit includes transmission RF circuits 103 c and 103 d and receptionRF circuits 104 c and 104 d instead of transmission RF circuits 103 aand 103 b and reception RF circuits 104 a and 104 b in FIG. 2A.

IF transfer circuit 151 separates the IF band control signal from IFcable 153, demodulates the control signal output from array controlcircuit 113, and outputs the demodulated control signal to transmissionRF circuits 103 c and 103 d and reception RF circuits 104 c and 104 d.

IF transfer circuit 151 also separates the transmission IF band signaland outputs it to transmission RF circuits 103 c and/or 103 d.Transmission RF circuits 103 c and 103 d modulate and amplify thetransmission IF band signal into a transmission RF signal. TransmissionRF circuits 103 c and 103 d also controls, based on a signal resultingfrom demodulation of the IF band control signal by IF transfer circuit151, the amplitude and phase of the transmission RF signal to performthe transmission directivity control.

In addition, while reception RF circuits 104 a and 104 b demodulate thereception RF signal into the reception baseband signal in FIG. 2A,reception RF circuits 104 c and 104 d demodulate the reception RF signalinto the reception IF band signal in FIG. 2B. IF transfer circuit 151multiplexes the received IF band signal with another signal, and outputsthe multiplexed signal to IF cable 153. IF transfer circuit 152demodulates the reception IF band signal, generates a reception basebandsignal, and outputs the signal to A/D converters 112 a and 112 b.

In the configuration of FIG. 2B, since a plurality of signals aremultiplexed and transmitted to IF cable 153, IF cable 153 can be longerthan in the configuration of FIG. 2A, so that PHY circuit 110 a and MACcircuit 120 can be installed apart from RF module circuit 109 a.However, it is considered that communication apparatuses 100 a, 200 a,and 300 a have an integral function even when PHY circuit 110 a and RFmodule circuit 109 a are arranged apart from each other, since a signaltransmitted over IF cable 153 is designed according to theconfigurations of PHY circuit 110 a and RF module circuit 109 a.

FIG. 3 illustrates an example of a BFT procedure according to the802.11ad standard. The BFT includes at least one of Sector Level Sweep(SLS) and Beam Refinement Protocol (BRP).

In SLS, the communication apparatuses switch the directivities of thetransmission antennas (referred to as “transmission sectors” or“transmission Antenna Weight Vectors (AWVs)) or the directivities of thereception antennas (referred to as “reception sectors” or “receptionAWVs”) for each packet to perform BFT. In BRP, the communicationapparatuses switch the transmission sectors or reception sectors withina training field in a packet to perform BFT.

Further, in SLS and BRP, the communication apparatuses transmit aresponse frame including information on a best transmission sectorobtained by training (referred to as “best sector”), to perform BFT.

Note that a communication apparatus that starts BFT is referred to as“initiator.” A communication apparatus that responds to a request fromthe initiator is referred to as “responder.”

When performing SLS, the initiator first performs initiator transmissionsector sweep (Initiator TXSS). In Initiator TXSS, the initiatortransmits sector sweep (SSW) frames 511, 512, and 513 while switchingthe transmission sectors for each of the SSW frames. The responderperforms responder transmission sector sweep (Responder TXSS) to respondto Initiator TXSS. In Responder TXSS, the responder transmits SSW frames521, 522, and 523 while switching the transmission sectors for each ofthe SSW frames.

The initiator transmits SSW Feedback (SSW-FB) frame 531 and theresponder transmits SSW Acknowledgement (SSW-ACK) frame 541 to completeSLS.

When performing BRP, the initiator transmits BRP frame 601 to theresponder. When receiving BRP frame 601, the responder transmits, to theinitiator, BRP frame 602 including a response depending on the type(described below) of a request included in BRP frame 601.

BRP is performed by repeatedly transmitting BRP frames between theinitiator and the responder (Beam Refinement Transaction (hereinafterreferred to as “BRT”)). BRP may include one or more subphases prior toBRT. The subphases include, by way of example, a setup subphase, aMultiple Sector Identifier (MID) subphase, a Beam Combining (BC)subphase, and an MID Capture (MIDC) subphase, and are performed bytransmission of BRP frames from the initiator and the responder as inBRT.

When the responder transmits a BRP frame containing no request, theinitiator may stop transmitting a BRP frame to end BRT to end BRP.

Note that, the initiator or the responder may include a request for aBRP frame in the SSW-FB or SSW-ACK frame to perform BRP subsequent toSLS. In FIG. 3, by way of example, the initiator sets the value of aTX-TRN-REQ subfield of SSW-FB frame 531 to 1 to request from theresponder that BRP be performed after completion of SLS to performtransmission BFT.

The initiator sets the value of an L-RX subfield of SSW-FB frame 531 to1 or greater (L-RX>0 in FIG. 3) to request from the responder that BRPbe performed after completion of SLS to perform reception BFT.

The initiator transmits, in the setup subphase, BRP frame 601 in which aCapability Request subfield is set to 1. The setup subphase ends whenthe responder and the initiator transmit BRP frames 604 and 605 in whichthe Capability Request subfields are set to 0.

The initiator transmits BRP frame 601 in which a TX-FBCK-REQ subfield isset to 1 and an SNR Requested subfield is set to 1.

In response to the fact that the SNR Requested subfield of BRP frame 601is set to 1, the responder includes a Channel Measurement Feedbackelement in BRP frame 602 and sets, in a SNR field of the ChannelMeasurement Feedback element, the value of a Signal to Noise Ratio (SNR)measured while BRP frame 601 is being received (i.e., the value of thereception quality). Note that the SNR may have a plurality of values.The responder sets an SNR Present subfield to 1 to notify the initiatorof validity of the value of the SNR field of the Channel MeasurementFeedback element.

In addition, the responder transmits the BRP frame in which values of atransmission sector ID and an antenna ID corresponding to the value ofthe SNR are included in a below-described Sector ID Order field of theChannel Measurement Feedback element. The responder sets a Sector IDOrder Present subfield to 1 to notify the initiator of validity of thevalue of the Sector ID Order field of the Channel Measurement Feedbackelement.

In this manner, in addition to notifying of the best sector, atransmission apparatus notifies of measurement results of receptionquality corresponding to a plurality of transmission sectors (that is, alist of measurement results) in the SNR field and the Sector ID Orderfield of the Channel Measurement Feedback element. Thus, a transmissionapparatus considers Sector IDs included in the list of measurementresults as candidate transmission sectors, and performs Beam RefinementTransaction to test combinations of the candidate transmission sectorsand reception sectors, so as to be capable of finding a truly bestsector with better communication quality than a provisional best sectorobtained by SLS.

FIG. 4 illustrates a SISO BRP TXSS procedure according to the 802.11aydraft standard. SISO BRP TXSS is one method for the initiator andresponder to perform the transmission and reception BFT using BPRframes. Unlike BRP of FIG. 3, the roles and the transmission order ofthe BRP frames are determined in advance, so that the processing timetaken for response by the initiator and the responder (time taken forprocessing after reception of a BRP frame until transmission of the nextBRP frame) can be shortened.

All of the frames transmitted to the initiator and the responder duringSISO BRP TXSS in FIG. 4 are BRP frames, and role names (e.g., “Setup”and “Enhanced directional multi-gigabit (EDMG) BRP-TX”) are illustratedin FIG. 4.

Setup BRP frames 701 and 702 are frames for notifying of start of theSISO BRP TXSS procedure by a BRP-TXSS field of the BRP frame set to 1and a TXSS-MIMO field set to 0. The initiator transmits Setup BRP frame701 to notify of the start of the SISO BRP TXSS procedure, and theresponder transmits Setup BRP frame 702 to accept the start of the SISOBRP TXSS procedure.

EDMG BRP-TX frame 703 is a BRP frame for performing the transmission BFTof the initiator.

Feedback BRP frame 704 is a frame for notification of the result of thetransmission BFT of the initiator. The responder transmits Feedback BRPframe 704 in which information on the best sector (best AWV) is includedin a BS-FBCK subfield of the Feedback BRP frame. The responder may alsoinclude a EDMG Channel Measurement Feedback element in Feedback BRPframe 704, include a plurality of combinations of AWVs, transmissionantenna IDs, and reception antenna IDs as information indicating theresult of transmission BFT in a EDMG Sector ID Order field, and includean SNR value for each of the combinations of the AWVs, transmissionantenna IDs, and reception antenna IDs in the SNR field of the ChannelMeasurement Feedback element.

The responder is capable of including a list of AWVs indicating theresult of transmission BFT in the EDMG Sector ID Order field as in theSector ID Order field of BRP frame 602 in FIG. 3.

The responder may also include training results (SNRs or receptionqualities) concerning a plurality of AWVs, such as the best AWV, thesecond best AWV, . . . , the n-th best AWV, for example, in the EDMGSector ID Order field.

The responder may also include, in the EDMG Sector ID Order field,training results (SNRs or reception qualities) concerning the AWVs forthe respective combinations of transmission antenna IDs and receptionantenna IDs, such as the best AWV for the combination (0,0) of atransmission antenna ID and a reception antenna ID, the best AWV for thecombination (0,1), the best AWV for the combination (1,0), and the bestAWV for the combination (1,1), for example.

EDMG BRP-RX frame 705 is a BRP frame for performing the reception BFT ofthe responder.

EDMG BRP-TX frame 706 and Feedback BRP frame 707 are BRP frames forperforming transmission BFT of the responder and for feedback,respectively. EDMG BRP-RX frame 708 is a BRP frame for performingreception BFT of the initiator. Note that transmission and reception ofEDMG BRP-TX frame 706, Feedback BRP frame 707, and EDMG BRP-RX frame 708may be omitted.

The initiator transmits Ack BRP frame 709 and notifies the responder ofthe end of the SISO BRP TXSS procedure. After transmitting the Ack BRPframe, the initiator changes the transmission AWV based on the value ofthe BS-FBCK field included in Feedback Ack frame 704. The initiator alsoreceives EDMG BRP-RX frame 708 to perform reception BFT, and changes thereception AWV of the initiator based on the result of the reception BFT.

After receiving the Ack BRP frame, the responder changes thetransmission AWV based on the value of the BS-FBCK field included inFeedback Ack frame 707. The responder also receives EDMG BRP-RX frame705 to perform reception BFT, and changes the reception AWV of theresponder based on the result of the reception BFT.

The initiator and the responder transmit and receive data using the bestsectors (AWVs) set by the SISO BRP TXSS procedure. By way of example,the initiator transmits single-stream (SISO) data frames 710 and 712using the optimal transmission AWV designated in the BS-FBCK field offeedback BRP frame 704. The initiator also receives BA (BlockAck) frames711 and 713 using the optimal reception AWV determined through receptionof EDMG BRP-RX frame 705.

FIGS. 5 and 6 illustrate examples of a SU-MIMO BFT procedure accordingto the draft 802.11ay standard. The SU-MIMO BFT procedure is one methodfor the initiator and the responder to perform the transmission andreception BFT with multiple antennas using BPR frames. The SU-MIMO BFTprocedure is performed prior to SU-MIMO data communication.

The SU-MIMO BFT procedure includes a SISO phase and a MIMO phase. TheSISO phase includes a method using a MIMO BRP TXSS procedure (FIG. 5)and a method using SISO Feedback Procedure (FIG. 6).

The procedure of FIG. 5 will be described. Setup BRP frames 801 and 802are frames for notifying of the start of the MIMO BRP TXSS procedure bya BRP-TXSS field of the BRP frame set to 1 and a TXSS-MIMO field setto 1. The initiator transmits Setup BRP frame 801 to notify of the startof the MIMO BRP TXSS procedure, and the responder transmits Setup BRPframe 802 to accept the start of the MIMO BRP TXSS procedure.

EDMG BRP-TX frame 803 is a BRP frame for performing transmission BFT ofthe initiator. When the initiator includes a plurality of transmissionantennas (antenna arrays) 101 a and 101 b, the initiator may transmit atraining pattern from each of transmission antennas 101 a and 101 b byswitching the transmission antennas during transmission of EDMG BRP-TXframe 803. In addition, the initiator may perform training for each oftransmission antennas 101 a and 101 b by transmitting a plurality ofBRP-TX frames 803 for each of transmission antennas 101 a and 101 b.Further, the initiator repeats transmission of BRP-TX frame 803depending on the number of reception antennas (antenna arrays) 101 a and101 b of the responder, so as to perform training for all combinationsof the transmission antennas of the initiator and the reception antennasof the responder.

Feedback BRP frame 804 is a frame for notification of the result oftransmission BFT of the initiator. The responder may also include theEDMG Channel Measurement Feedback element in Feedback BRP frame 804,include a plurality of combinations of AWVs, transmission antenna IDs,and reception antenna IDs as information indicating the result oftransmission BFT in a EDMG Sector ID Order field, and include an SNRvalue for each of the combinations of the AWVs, transmission antennaIDs, and reception antenna IDs in the SNR field of the ChannelMeasurement Feedback element.

In the EDMG Sector ID Order field, the initiator feeds back a pluralityof AWVs for each combination of the transmission antennas of theinitiator and the reception antennas of the responder. When the numberof AWVs for each of the combinations is less than or equal to 16, theinitiator selects all the AWVs, and when the number of AWVs is greaterthan 16, the initiator selects 16 AWVs (e.g., 16 AWVs with goodreception quality), and includes the AWVs in the EDMG Sector ID Orderfield.

The responder then transmits EDMG BRP-TX frame 805 and the initiatorreceives Feedback BRP frame 806. The initiator thus performs training aswith EDMG BRP-TX frame 803 and Feedback BRP frame 804. Thereafter, theresponder transmits Ack BRP frame 807 to complete the MIMO BRP TXSSprocedure.

In the MIMO phase, the initiator and the responder transmit MIMO BFSetup BRP frames 851 and 852 for notification of the start of the MIMOphase. Note that, based on the feedback results (Feedback BRP frames 804and 806) received in the SISO phase, the initiator and the responderinclude a list of the combinations of the transmission and receptionantennas and AWVs for performing training of MIMO BFT in MIMO BF SetupBRP frames 851 and 852.

The initiator and the responder transmit EDMG BRP-RX/TX frames 853 and854, respectively, to perform the MIMO BFT training. This is done byincluding MIMO training patterns (simultaneous transmission of trainingsignals by multiple antennas) in EDMG BRP-RX/TX frames 853 and 854 basedon the combinations of the transmission and reception antennas and AWVsincluded in MIMO BF Setup BRP frames 851 and 852.

The initiator and the responder transmit MIMO BF Feedback frames 855 and856 to complete the MIMO phase and SU-MIMO BFT.

After SU-MIMO BFT is completed, the initiator and the responder transmitSU-MIMO data frames (not illustrated) using the combinations of thetransmission and reception antennas and AWVs as notified by MIMO BFFeedback frames 855 and 856.

The procedure in FIG. 6 will be described. Since the procedure in theMIMO phase is the same as that in FIG. 5, descriptions thereof areomitted.

When SISO BFT 811 has been completed prior to the start of SU-MIMO BFT,the initiator and the responder may perform the SISO Feedback procedureinstead of MIMO BFT TXSS for the SISO phase. SISO BFT 811 may, forexample, be SLS (see FIG. 3), SISO BRP TXSS (see FIG. 4), or MIMO BRPTXSS (see FIG. 5).

When performing SISO BFT 811, the initiator performs training for allthe combinations of the transmission antennas of the initiator and thereception antennas of the responder. The responder retains the result.For example, BF control circuit 124 retains SNR values for thecombinations of the transmission and reception antennas and AWVs in thememory.

Similarly, when performing SISO BFT 811, the responder performs trainingfor all the combinations of the transmission antennas of the responderand the reception antennas of the initiator. The initiator retains theresult.

Note that, the initiator and the responder in SU-MIMO BFT may be thesame as the initiator and the responder in SISO BFT, or may also bereversed (replaced with each other).

The initiator and the responder include the EDMG Channel MeasurementFeedback elements respectively in Feedback BRP frames 812 and 813,include one or more combinations of AWVs, transmission antenna IDs, andreception antenna IDs as information indicating the result oftransmission BFT in each of the EDMG Sector ID Order fields, and includeSNR values for respective combinations of the AWVs, transmission antennaIDs, and reception antenna IDs in the SNR fields of the ChannelMeasurement Feedback elements. This corresponds to the informationcontained in Feedback BRP frames 806 and 804 of FIG. 5.

Based on the received feedback results (Feedback BRP frames 812 and813), the initiator and the responder include, in MIMO BF Setup BRPframes 851 a and 852 a, a list of the combinations of the transmissionand reception antennas and AWVs for performing training of MIMO BFT.

Note that there may be a time interval between SISO BFT 811 and FeedbackBRP frame 812. For example, another communication apparatus (notillustrated) may perform data communication after SISO BFT 811.

As is understood, the SISO Feedback procedure of FIG. 6 can be completedin a short time since the number of frames to be transmitted andreceived is smaller than in MIMO BRP TXSS of FIG. 5. However, theinitiator and the responder need to retain the training results for thecombinations of the transmission and reception antennas and the AWVs inSISO BFT.

FIGS. 7 and 8 illustrate examples of a MU-MIMO BFT procedure accordingto the 802.11ay draft standard. The MU-MIMO BFT procedure is one methodfor the initiator and a plurality of responders to perform transmissionwith multiple antennas and BFT with one or more reception antennas usingBPR frames. The MU-MIMO BFT procedure is performed prior to MU-MIMO datacommunication.

The MU-MIMO BFT procedure includes a SISO phase and a MIMO phase. TheMIMO phase is a procedure of training for MIMO transmissions like theMIMO phase of SU-MIMO BFT. Detailed description is omitted. The SISOphase includes an Initiator TXSS subphase and a SISO Feedback subphase(see FIG. 7), but the Initiator TXSS subphase may sometimes be omitted(FIG. 8).

The procedure of FIG. 7 will be described. In FIG. 7, the initiator(e.g., communication apparatus 100), responder 1 (e.g., communicationapparatus 200), and responder 2 (e.g., communication apparatus 300)perform MU-MIMO BFT.

In the Initiator TXSS subphase, the initiator transmits a plurality ofShort SSW frames 901 and 902 while changing transmission sectors foreach of the Short SSW frames. Responder 1 and responder 2 measure andretain reception qualities of Short SSW frames 901 and 902. For example,BF control circuit 124 retains SNR values for the combinations of thetransmission and reception antennas and sectors in the memory.

In the SISO Feedback subphase, the initiator transmits Poll BRP framesto the respective responders and asks for responses by Feedback BRPframes. The initiator transmits Poll BRP frame 911 to responder 1.

Responder 1 includes the EDMG Channel Measurement Feedback element inFeedback BRP frame 912, includes a plurality of combinations of AWVs,transmission antenna IDs, and reception antenna IDs as informationindicating the result of transmission BFT in the EDMG Sector ID Orderfield, and includes an SNR value for each of the combinations of theAWVs, transmission antenna IDs, and reception antenna IDs in the SNRfield of the Channel Measurement Feedback element. Responder 1 alsoincludes an EDMG BRP Request element in Feedback BRP frame 912, andincludes, in a L-TX-RX field and a Requested EDMG TRN UNIT M field,information on the number of reception AWVs for which training isperformed in the MIMO phase.

The initiator transmits Poll BRP frame 913 to responder 2. Responder 2includes the EDMG Channel Measurement Feedback element and the EDMG BRPRequest element in Feedback BRP frame 914 and transmits the Feedback BRPframe. Note that since Feedback BRP frame 914 is the same as FeedbackBRP frame 912, other descriptions are omitted.

In the MIMO phase, MIMO training is performed for the combinations ofthe transmission and reception antennas and AWVs specified by feedbackinformation included in Feedback BRP frames 912 and 914 and for thenumber of reception AWVs, so as to determine the combinations oftransmission and reception antennas and AWVs used for MU-MIMO datacommunication.

The procedure of FIG. 8 will be described. In a case where the initiatorhas already completed SISO BFT (e.g., SISO BFTs 921 and 922) with bothresponders 1 and 2, the Initiator TXSS subphase may be omitted.

Responder 1 performs SISO BFT 921 with the initiator and retains thetraining result. The detail of the SISO BFT is the same as SISO BFT 811of FIG. 6. Responder 2 performs SISO BFT 922 with the initiator andretains the training result.

Based on the training results retained in SISO BFT 921, responder 1includes a list of combinations of transmission and reception antennasand AWVs, and SNRs for each of the combinations in Feedback BRP frame912 a and transmits the Feedback BRP frame.

Based on the training results retained in SISO BFT 922, responder 2includes a list of combinations of transmission and reception antennasand AWVs, and SNRs for each of the combinations in Feedback BRP frame914 a and transmits the Feedback BRP frame.

Since MIMO phase 950 of FIG. 8 is the same as that of FIG. 7,descriptions thereof are omitted.

Note that, there may be a time interval between the end of SISO BFT 921and the start of SISO BFT 922 and between the end of SISO BFT 922 andthe start of the SISO phase. For example, another communicationapparatus (not illustrated) may perform data communication after SISOBFT 922.

As is understood, the SISO phase of FIG. 8 can be completed in a shortertime because the number of frames to be transmitted and received issmaller than in the SISO phase of FIG. 7. Note that, the initiator andthe responder retain the training results for the combinations of thetransmission and reception antennas and AWVs in SISO BFT.

FIG. 9 illustrates a format of the BRP frame used in FIGS. 3 to 8. TheBRP frame includes a Frame Control field, Duration field, Address1field, Address2 field, Category field, Unprotected Directionalmulti-gigabit (DMG) Action field, Dialog Token field, BRP Request field,DMG Beam Refinement element, Channel Measurement Feedback element, EDMGPartial Sector Level Sweep element, EDMG BRP Request element, and EDMGChannel Measurement Feedback element.

The Frame Control field, Duration field, Address1 field, Address2 field,Category field, Unprotected DMG Action field, Dialog Token field, andBRP Request field are abbreviated as <fields>.

The Channel Measurement Feedback element, EDMG Partial Sector LevelSweep element, EDMG BRP Request element, and EDMG Channel MeasurementFeedback element are optional elements and may be omitted.

The BRP frame is of a single format illustrated in FIG. 9, but functionsas frames having different roles (e.g., Setup BRP frame, Feedback BRPframe, and the like) as illustrated in FIGS. 3 to 8.

The BFT procedures according to the 802.11ad standard have beendescribed above. However, since the BRP frame format is the same, it isdifficult for communication apparatus 100 (responder) to distinguishwhether the received BRP frame is BRP frame 601 of FIG. 3 (the initiatorintends the Setup subphase of SISO BRP), the Setup BRP frame of FIG. 4(the initiator intends SISO BRP TXSS), the Setup BRP frame of FIG. 5(the initiator intends MIMO BRP TXSS of SU-MIMO), the Feedback BRP frameof FIG. 6 (the initiator intends the SISO Feedback procedure ofSU-MIMO), or the Poll BRP frame of FIG. 8 (the initiator intends theSISO phase of MU-MIMO).

Further, since TXSS of FIGS. 6 and 8 intends SISO BFT, it is difficultfor the responder to know in advance whether or not the SISO phase ofSU-MIMO BFT after TXSS is carried out (see FIG. 6), and whether or notMU-MIMO BFT in which the Initiator TXSS subphase is omitted is carriedout (see FIG. 8).

For example, in TXSS of FIG. 6, when the responder performs a selectionof the best sector with the intention for SISO BFT, it is difficult toinclude combinations of transmission and reception antennas and AWVs,and the information on SNRs in Feedback BRP frame 813 to transmit theFeedback BRP frame. That is, it is difficult for the responder torespond appropriately even when the responder can determine thatFeedback BRP frame 812 is intended for the SISO Feedback procedure.

Hereinafter, a method in which communication apparatus 100 distinguishesthe intention of the BRP frame received, and appropriately respondsthereto will be described.

Embodiment 1

According to the type (FIG. 3, 4, 5, 6, 7, or 8) of the BFT procedure tobe carried out using the BRP frame, communication apparatus 100determines the types of element to be included in the BRP frame to betransmitted first, and transmits the BRP frame without including otheroptional elements in the BRP frame. Thus, the responder can distinguishthe type of the BFT procedure.

FIGS. 10A to 10D and FIG. 11 illustrate formats of the BRP frame to betransmitted first when communication apparatuses 100 (initiator andresponder) perform the BFT procedure of FIG. 3, 4, 5, 6, 7, or 8. FIGS.10A to 10D illustrate elements included in the BRP frame, and FIG. 11illustrates values of the elements, fields, and subfields. Note that,some of the elements, fields, and subfields are illustrated, and othersare omitted in FIG. 11.

As illustrated in FIG. 10A, when performing BRP of SISO TXSS (see FIG.3), the initiator includes a 7-octet DMG Beam Refinement element in BRPframe 601 and transmits the BRP frame in the Setup subphase.

As illustrated in FIG. 10B, when the initiator performs SISO BRP TXSS(see FIG. 4) or MIMO BRP TXSS (see FIG. 5), the initiator includes a10-octet DMG Beam Refinement element and the EDMG BRP Request element inBRP frame 701 or 801 and transmits the BRP frame. As illustrated in FIG.11, the initiator sets the value of the BRP-TXSS field to 1. Further,the initiator sets the value of the TXSS-MIMO field of BRP frame 701 to0 in the case of SISO BRP TXSS or sets the value of the TXSS-MIMO fieldof BRP frame 801 to 1 in the case of MIMO BRP TXSS.

Note that the 7-octet DMG Beam Refinement element illustrated in FIG.10A is defined in the 11ad standard, and the 10-octet DMG BeamRefinement element illustrated in FIG. 10B is defined in the flay draftstandard.

As illustrated in FIG. 10C, when performing the SISO Feedback procedureof SU-MIMO (see FIG. 6), the initiator includes the 10-octet DMG BeamRefinement element, Channel Measurement Feedback element, and EDMGChannel Measurement Feedback element in BRP frame 812 and transmits theBRP frame. As illustrated in FIG. 11, the initiator sets the value ofthe BRP-TXSS field to 1.

Further, the initiator sets each of the SNR Requested field and SectorID Order subfield of the FBCK-REQ field to 1. Accordingly, the responderis requested to feed back a list of AWVs and SNRs. The initiator alsosets the value of each of the TXSS-FBCK-REQ field, the SNR Presentsubfield of the FBCK-TYPE field, and the Sector ID Order Presentsubfield to 1.

With this setting, the initiator notifies of the validity of the valueof the SNR field of the Channel Measurement Feedback element of BRPframe 812 and the value of the EDMG Sector ID Order field of the EDMGChannel Measurement Feedback element.

As illustrated in FIG. 10D, when performing the SISO Feedback subphaseof MU-MIMO (see FIGS. 7 and 8), the initiator includes the 10-octet DMGBeam Refinement element in BRP frame 911 or 911 a and transmits the BRPframe. The initiator sets the values of the TXSS-FBCK-REQ field, the SNRPresent subfield of the FBCK-TYPE field, and the Sector ID Order Presentsubfield to 1.

The initiator sets, in a Length field in the DMG Beam Refinementelement, the number of octets of the DMG Beam Refinement element minus 2octets (the number of octets of the Element ID field plus the number ofoctets of the Length field).

FIG. 12 is a flowchart illustrating a procedure for distinguishing thetype of the BFT procedure (FIG. 3, 4, 5, 6, 7, or 8) when the responderreceives the BRP frame.

At step S1001, the responder receives the BRP frame.

At step S1002, the responder determines whether or not the DMG BeamRefinement element is 10 octets or greater in length (the value of theLength field is 8 or greater). In the case of Yes, the procedureproceeds to step S1003. In the case of No, the procedure proceeds tostep S1020.

Note that, at step S1002, the responder may determine whether or not thevalue of an EDMG Extension Flag field is 1 instead of determining thelength of DMG Beam Refinement element. The case where the value of theEDMG Extension Flag field is 1 corresponds to “Yes.” The case where thevalue of the EDMG Extension Flag field is 0 or the field does not existcorresponds to “No.”

At step S1003, the responder determines whether or not the EDMG BRPRequest element exists. In the case of Yes, the procedure proceeds tostep S1004. In the case of No, the procedure proceeds to step 1006.

At step S1004, the responder determines whether or not both of thevalues of the BRP-TXSS field and of the TXSS-Initiator field are 1. Inthe case of Yes, the procedure proceeds to step S1005. In the case ofNo, the procedure proceeds to step 1020.

At step S1005, the responder determines whether or not the value of theTXSS-MIMO field is 0. In the case of Yes, the procedure proceeds to stepS1011. In the case of No, the procedure proceeds to step 1013.

At step S1006, the responder determines whether or not the EDMG ChannelMeasurement Feedback element exists. In the case of Yes, the procedureproceeds to step S1015. In the case of No, the procedure proceeds tostep 1017.

Note that at step S1006, the responder may determine whether or not theChannel Measurement Feedback element exists instead of determiningwhether or not the EDMG Channel Measurement Feedback element exists. Theresponder may also determine whether or not the value of the EDMGChannel Measurement Present subfield is 1. The responder may alsodetermine whether or not each subfield of FBCK-TYPE field contains anon-zero value.

When the procedure proceeds to step S1011 based on the abovedeterminations, the responder determines that the received BRP frame isSetup BRP frame 701 of SISO BRP TXSS (FIG. 4). At step S1012, Setup BRPframe 702 is transmitted.

When the procedure proceeds to step S1013, the responder determines thatthe received BRP frame is Setup BRP frame 801 of MIMO BRP TXSS (FIG. 5).At step S1014, Setup BRP frame 802 is transmitted.

When the procedure proceeds to step S1015, the responder determines thatthe received BRP frame is Feedback BRP frame 812 of the SISO Feedbackprocedure of SU-MIMO BFT. At step S1016, Feedback BRP frame 813 istransmitted.

When the procedure proceeds to step S1017, the responder determines thatthe received BRP frame is Poll BRP frame 911 or 911 a of MU-MIMO BFT. Atstep S1018, Feedback BRP frame 912 or 912 a is transmitted.

When the procedure proceeds to step S1020, the responder determines thatthe received BRP frame is not of the EDMG BRP procedure (FIG. 4, 5, 6, 7or 8), and transmits BRP frame 602 to perform the SISO BRP procedure ofFIG. 3.

FIG. 13 illustrates the types of SISO BFT that can be used incombination with the SISO Feedback procedure of SU-MIMO BFT when theinitiator uses the BRP frame of FIG. 10A, 10B, 10C, 10D, or 11 as theleading BRP frame of the procedure.

By way of example, communication apparatus (STA) 100 performs SLS ofFIG. 3 with STA 200 and performs the SISO Feedback procedure and MIMOPhase of FIG. 6 to complete SISO BFT and SU-MIMO BFT.

By way of another example, STA 100 performs SISO BRP TXSS of FIG. 4 withSTA 200 and performs the SISO Feedback procedure and MIMO Phase of FIG.6 to complete SISO BFT and SU-MIMO BFT.

By way of another example, STA 100 performs MIMO BRP TXSS and MIMO Phaseof FIG. 5 with STA 200 to complete the first SU-MIMO BFT.

Further, when the first SU-MIMO BFT is completed, STA 100 may performthe SISO Feedback procedure and MIMO Phase of FIG. 6 to complete thesecond SU-MIMO BFT.

For example, in a case where there is any obstruction between STA 100and STA 200 when STA 100 and STA 200 perform SU-MIMO data transmissionafter completion of the first SU-MIMO BFT, the STAs include combinationsof transmission and reception antennas and AWVs and SNRs retained at theoccasion of the first SU-MIMO BFT in Feedback BRP frames 812 and 813 ofFIG. 6 and transmit the Feedback BRP frames, so as to complete SU-MIMOBFT. Thus, in the second SU-MIMO BFT, it is possible to omit MIMO BRPTXSS and SISO TXSS (811 in FIG. 6), and to shorten the time taken forcarrying out SU-MIMO BFT.

FIG. 14 illustrates a procedure for communication apparatuses (initiatorand responder) to perform SU-MIMO BFT of FIG. 6 using the BRP frameillustrated in one of FIGS. 10A to 10D and FIG. 11. The same BRP framesas in FIG. 6 are provided with the same reference numerals, and thedescription thereof is omitted.

The initiator and the responder transmit Capability information 401 and402 prior to starting SU-MIMO BFT.

The Capability information includes a list of functions supported by theinitiator and the responder, and includes a field indicating whether ornot SU-MIMO and MU-MIMO are to be supported. Note that, the initiatorand the responder may include, in Capability information 401 and 402,bits respectively indicating whether or not SISO BRP TXSS (FIG. 4) issupported, whether or not MIMO BRP TXSS (FIG. 5) is supported, whetheror not the SISO Feedback procedure (FIG. 6) is supported, and whether ornot MU-MIMO BFT (FIG. 8) in which Initiator TXSS is omitted issupported.

When the Capability information notifies the initiator and the responderthat the initiator and the responder support SU-MIMO, the initiator andthe responder perform SISO BFT while carrying out TXSS 811 a, andmeasure and retain combinations of transmission and reception antennasand AWVs used for SU-MIMO BFT and the value of SNR for each of thecombinations as a result of TXSS training for MIMO.

The initiator and the responder include the retained result of TXSStraining for MIMO in Feedback BRP frames 812 and 813 and transmit theFeedback BRP frames, so that SU-MIMO BFT can be carried out correctly.

The initiator and responder may perform TXSS 811 a prior to transmittingCapability information 401 and 402. Accordingly, when the initiatorcarries out TXSS 811 a after transmissions of Capability information 401and Capability information 402, the initiator may transmit Feedback BRPframe 812 to start the SISO Feedback procedure.

Before performing TXSS 811 a with the responder, the initiatortransmits, to the responder, the Capability information includinginformation indicating whether or not each of SU-MIMO and MU-MIMO is tobe supported. Accordingly, the responder can retain the result of TXSStraining for MIMO while TXSS 811 a is being carried out, and can includethe result of TXSS training for MIMO in Feedback BRP frame 813.

Note that, when receiving the BRP frame, the responder may respondthereto using the format of common Feedback BRP frame 981 instead ofperforming a response (Setup BRP frame 602, Setup BRP frame 701, SetupBRP frame 802, Feedback BRP frame 813, or Feedback BRP frame 912) inaccordance with the intention of the received BRP frame received usingthe flowchart of FIG. 12.

FIG. 15 illustrates a format of common Feedback BRP frame 981. Theresponder includes the 10-octet DMG Beam Refinement element, ChannelMeasurement Feedback element, EDMG BRP Request element, and EDMG ChannelMeasurement Feedback element in BRP frame 981.

The responder sets the value of EDMG Extension Flag field of DMG BeamRefinement element of BRP frame 981 to 1, the value of EDMG ChannelMeasurement Present field to 1, and the values of SNR Present subfieldand Sector ID Order Present subfield of FBCK-TYPE field to 1.

When the responder supports SU-MIMO or MU-MIMO, the responder feedsback, in the EDMG Sector ID Order field of the EDMG Channel MeasurementFeedback element, a plurality of AWVs for each combination oftransmission antennas of the initiator and reception antennas of theresponder. When the number of AWVs in each of the combinations of thetransmission and reception antennas is less than or equal to 16, theinitiator selects all the AWVs to include the AWVs in the EDMG Sector IDOrder field, and when the number of AWVs is greater than 16, theinitiator selects 16 AWVs (e.g., 16 AWVs of high reception quality) toinclude the AWVs in the EDMG Sector ID Order field. This information isused as essential information in SU-MIMO BFT and MU-MIMO BFT, but may beused for SISO BFT.

The responder includes the SNR value for each of the AWVs in the SNRfield of the Channel Measurement Feedback element.

The responder includes, in an L-RX field and the Requested EDMG TRN UNITM field of the EDMG BRP Request element, information on the number ofreception AWVs for which training is performed when the responderreceives EDMG BRP-RX frame 705 of SISO BRP TXSS.

When the responder supports MU-MIMO, the responder includes, in theL-TX-RX field and the Requested EDMG TRN UNIT M field of the EDMG BRPRequest element, the information on the number of reception AWVs forwhich training is performed in the MIMO phase of MU-MIMO BFT.

As described above, the responder responds, using common Feedback BRPframe 981, to the first BRP frame transmitted by the initiator, so thatan appropriate response can be made, whichever one of SISO BFT, SU-MIMOBFT, and MU-MIMO BFT the initiator intends.

Embodiment 2

Communication apparatus 100 includes, in the BRP frame to be transmittedfirst, a field indicating the type of SISO, SU-MIMO, or MU-MIMOdepending on the type of the BFT procedure to be carried out using theBRP frame (FIG. 3, 4, 5, 6, 7, or 8) and transmits the BRP frame. Theresponder can distinguish the type of the BFT procedure (FIG. 3, 4, 5,6, 7, or 8) based on a combination of the field indicating the type andthe other fields.

FIG. 16 illustrates a format of a BRP frame of Embodiment 2. Unlike theBRP frame of FIG. 9, the DMG Beam Refinement element includes a BFTraining Type field. The value of 0 of the BF Training Type fieldindicates SISO, the value of 1 indicates SU-MIMO, and the value of 2indicates MU-MIMO. The value of 3 is a reserved value.

When performing the Setup subphase (FIG. 3) of SISO BRP, the initiatorsets the value of the BF Training Type field of BRP frame 601 to 0(SISO).

When performing SISO BRP TXSS (FIG. 4), the initiator sets the value ofthe BF Training Type field of Setup BRP frame 701 to 0 (SISO).

When performing MIMO BRP TXSS (FIG. 5), the initiator sets the value ofthe BF Training Type field of Setup BRP frame 801 to 1 (SU-MIMO).

When performing the SISO Feedback procedure of SU-MIMO (FIG. 6), theinitiator sets the value of the BF Training Type field of Feedback BRPframe 812 to 1 (SU-MIMO).

When performing the SISO Feedback subphase (FIG. 8) of MU-MIMO, theinitiator sets the value of the BF Training Type field of Poll BRP frame911 a to 2 (MU-MIMO).

FIG. 17 illustrates a procedure for the initiator and the responder toperform SISO BRP TXSS and SU-MIMO BFT using the BRP frame of FIG. 16.The same BRP frames as those in FIGS. 4 and 14 are provided with thesame reference numerals, and the description thereof is omitted.

The initiator sets the BF Training Type field of Setup BRP frame 701 ato 0 and transmits the Setup BRP frame in order to perform SISO BRPTXSS.

The responder sets the BF Training Type field of Setup BRP frame 702 ato 0 and transmits the Setup BRP frame to the initiator in order torespond to the initiator that SISO BRP TXSS can be carried out.

When SISO BRP TXSS is completed, the initiator sets the BF Training Typefield of Feedback BRP frame 812 a to 1 and transmits the Feedback BRPframe in order to perform the SISO Feedback procedure of SU-MIMO.

The responder sets the BF Training Type field of Feedback BRP frame 813a to 1 and transmits the Feedback BRP frame in order to respond to theinitiator that the SISO Feedback procedure can be carried out.

FIG. 18 is a flowchart illustrating a procedure for distinguishing thetype of the BFT procedure (FIG. 3, 4, 5, 6, 7, or 8) when the responderreceives the BRP frame of FIG. 16. The same processes as those in FIG.12 are provided with the same reference numerals, and the descriptionthereof is omitted.

In the case of No at step S1003 or step S1004, the responder proceeds tostep S1103 a.

At step S1103 a, the responder proceeds to step S1020 when the value ofthe BF Training Type field is 0. In this case, the responder determinesthat the received BRP frame is a BRP frame for SISO BFT, but not forSISO BRP TXSS or MIMO BRP TXSS.

At step S1103 a, the responder proceeds to step S1103 b when the valueof the BF Training Type field is other than 0.

At step S1103 b, when the value of the BF Training Type field is 1, theresponder proceeds to step S1015. In this case, the responder determinesthat the received BRP frame is a BRP frame that is for SU-MIMO and thatnotifies of the start of the SISO Feedback procedure.

At step S1103 b, the responder proceeds to step S1103 c when the valueof the BF Training Type field is other than 1.

At step S1103 c, the responder proceeds to step S1017 when the value ofthe BF Training Type field is 2. In this case, the responder determinesthat the received BRP frame is a BRP frame that is for MU-MIMO and thatnotifies of the start of SISO Feedback Subphase.

At step S1103 c, the responder proceeds to step S1030 when the value ofthe BF Training Type field is other than 2. In this case, the responderdetermines that the received BRP frame is a frame notifying of the startof an unsupported procedure (for example, part of a future extended 11aystandard).

When starting SISO BFT, SU-MIMO BFT, or MU-MIMO BFT using the BRP frame,the initiator includes the BF Training Type field in the BRP frame andtransmits the BRP frame. The responder distinguishes the type of the BFTprocedure by using the procedure of FIG. 18. The responder candistinguish the type of the BFT procedure (FIG. 3, 4, 5, 6, 7, or 8), sothat it is possible to combine different types of BFT procedures tocarry out BFT so as to shorten the time taken to carry out BFT.

When using the format of the BRP frame of FIG. 16 at the start of theBRP procedure, the initiator may include an optional (dispensable)element in the BRP frame and transmit the BRP frame unlike the casewhere the frame format of one of FIGS. 10A to 10D is used. By way ofexample, the initiator may include the Channel Measurement Feedbackelement and the EDMG Channel Measurement Feedback element in Setup BRPframe 701 of SISO BRP TXSS, and may include combinations of transmissionand reception antennas and AWVs and the information on SNRs to betransmitted in the SISO Feedback procedure of SU-MIMO. Thus, theinitiator can omit the SISO Feedback procedure of SU-MIMO BFT and startthe MIMO phase after completing SISO BRP TXSS, so as to reduce the timetaken to carry out SU-MIMO BFT.

Further, the responder distinguishes the type of BFT by using theprocedure of FIG. 18. Thus, the type of BFT can be correctlydistinguished even when an optional (dispensable) element is included inthe BRP frame transmitted from the initiator first at the start of theBRP procedure, so that SISO BRP TXSS can be correctly carried out whenthe Channel Measurement Feedback element and the EDMG ChannelMeasurement Feedback element are included in Setup BRP frame 701 of SISOBRP TXSS as described above.

Note that, in the BRP frame format of FIG. 16, the initiator may set thevalue of the BF Training Type field to 0 when performing SISO BRP TXSS(FIG. 4) or MIMO BRP TXSS (FIG. 5), set the value of the BF TrainingType field to 1 when performing the SISO Feedback Procedure of SU-MIMOBFT, and set the value of the BF Training Type field to 2 whenperforming the SISO Feedback subphase of MU-MIMO BFT.

FIG. 19 illustrates an example of a format of the BRP frame other thanthat illustrated in FIG. 16. Unlike FIG. 16, the BF Training Type fieldhas one bit.

The initiator sets the value of the BF Training Type field to 0 whenperforming SISO BFT (MIMO BRP TXSS of FIG. 3, 4 or 5). When MIMO BFT(FIG. 6, 7, or 8) is performed, the value of the BF Training Type fieldis set to 1.

Note that, while a description is given of a case where MIMO BRP TXSS ofFIG. 5 is regarded as SISO BFT and the value of the BF Training Typefield is set to 0, the same description applies to a case where MIMO BRPTXSS is regarded as MIMO BFT and the value of the BF Training Type fieldis set to 1.

FIG. 20 is a flowchart illustrating a procedure for distinguishing thetype of the BFT procedure (FIG. 3, 4, 5, 6, 7, or 8) when the responderreceives the BRP frame of FIG. 19. The same processes as those in FIG.12 are provided with the same reference numerals, and the descriptionthereof is omitted.

In the case of No at step S1003 or step S1004, the responder proceeds tostep S1203.

At step S1203, the responder proceeds to step S1020 when the value ofthe BF Training Type field is 0. In this case, the responder determinesthat the received BRP frame is a BRP frame for SISO BFT, but not forSISO BRP TXSS and MIMO BRP TXSS.

At step S1203, the responder proceeds to step S1006 when the value ofthe BF Training Type field is 1. In this case, the responder determinesthat the received BRP frame is a BRP frame for SU-MIMO BFT or MU-MIMOBFT. The processing of the responder at step S1006 is the same as thatin FIG. 12.

Note that, in the BRP frame format of FIG. 19, the initiator may set thevalue of the BF Training Type field to 1 when performing the SISOFeedback Procedure of SU-MIMO BFT or the SISO Feedback subphase ofMU-MIMO BFT, or may otherwise set the value of the BF Training Typefield to 0.

Note also that, in the BRP frame format of FIG. 19, the initiator mayset the value of the BF Training Type field to 1 when performing theSISO Feedback subphase of MU-MIMO BFT, or may otherwise set the value ofthe BF Training Type field to 0. As with S1003 of FIG. 12 and instead ofdetermining whether or not the value of BF Training Type is 0 at stepS1203 of FIG. 20, the responder may proceed to step S1020 b when theEDMG BRP Request element exists and to step S1006 when the EDMG BRPRequest element does not exist, and at step S1006, the responder mayproceed to step S1015 when the value of the BF Training Type field is 0and to step S1017 when the value of the BF Training Type field is 1.

When starting SISO BFT, SU-MIMO BFT, or MU-MIMO BFT using the BRP frame,the initiator includes the BF Training Type field in the BRP frame andtransmits the BRP frame. The responder distinguishes the type of the BFTprocedure by using the procedure of FIG. 18. The responder candistinguish the type of the BFT procedure (FIG. 3, 4, 5, 6, 7, or 8), sothat it is possible to combine different types of BFT procedures tocarry out BFT so as to shorten the time taken to carry out BFT.

The initiator uses the BRP frame of FIG. 19 instead of the BRP frame ofFIG. 16 first in the BRP procedure. Accordingly, the number of bits ofthe BF Training Type field may be smaller and a larger number ofReserved bits can be left, so that the BRP frame of FIG. 19 is easy tobe functionally extended in the future.

Embodiment 3

Communication apparatus 100 uses the feedback value transmitted in theSISO phase of SU-MIMO BFT (see FIG. 6) for Beam Refinement Transactionof SISO BFT. The Setup subphase in BRP for SISO training (see FIG. 3)can be omitted and training can thus be completed early.

FIG. 21 illustrates an example of a procedure for the initiator and theresponder to perform SISO BFT and SU-MIMO BFT. The same BRP frames asthose in FIGS. 4, 6, and/or 17 are provided with the same referencenumerals, and the description thereof is omitted.

The initiator and the responder perform SISO BFT (TXSS 811) and SU-MIMOBFT (including the SISO Feedback procedure and MIMO phase) as in FIG. 6.Note that, the initiator may use the BRP frames of FIGS. 10A to 10D, 16,and/or 19 in the SISO Feedback procedure.

After completing SU-MIMO BFT, the initiator carries out Beam RefinementTransaction (BRP frames 606, 607, and 608).

When carrying out Beam Refinement Transaction, the initiator and theresponder refer to the values of the Channel Measurement Feedbackelement and EDMG Channel Measurement Feedback field included in FeedbackBRP frames 812 a and 813 a (the values of the EDMG Sector ID Order fieldand the SNR field) so as to determine the AWV with which Beam RefinementTransaction is to be performed. Accordingly, the initiator and theresponder can omit the Setup subphase of SISO BRP (see FIG. 3) prior toperforming Beam Refinement Transaction.

The initiator and the responder complete Beam Refinement Transaction tocomplete SISO BFT.

The procedure of FIG. 21 makes it possible for the initiator and theresponder to carry out SISO BFT and SU-MIMO BFT combined with eachother, and to omit the Setup subphase of SISO BRP to reduce the timetaken to carry out both SISO BFT and SU-MIMO BFT.

(Modification 1 of Embodiment 3)

Communication apparatuses 100 use the feedback value transmitted in theSISO phase of SU-MIMO BFT (see FIG. 6) for Beam Refinement Transactionof SISO BFT, and insert and carry out SISO BFT (Beam RefinementTransaction) between the SISO phase and the MIMO phase. The Setupsubphase in BRP for SISO training (see FIG. 3) can be omitted andtraining can be thus completed early.

FIG. 22 illustrates an example of a procedure for the initiator and theresponder to perform SISO BFT and SU-MIMO BFT. The same BRP frames asthose in FIGS. 4, 6, and/or 17 are provided with the same referencenumerals, and the description thereof is omitted.

The initiator and the responder perform SISO BFT (TXSS 811) and SU-MIMOBFT (the SISO Feedback procedure) as in FIG. 6. Note that, the initiatormay use the BRP frames of FIGS. 10A to 10D, 16, and/or 19 in the SISOFeedback procedure.

After the SISO Feedback procedure is completed, the initiator startsBeam Refinement Transaction of SISO BRP. When carrying out BeamRefinement Transaction, the initiator and the responder refer to thevalues of the Channel Measurement Feedback element and EDMG ChannelMeasurement Feedback field included in Feedback BRP frames 812 a and 813a (the values of the EDMG Sector ID Order field and the SNR field) so asto determine the AWV with which Beam Refinement Transaction is to beperformed. Accordingly, the initiator and the responder can omit theSetup subphase of SISO BRP (see FIG. 3) prior to performing BeamRefinement Transaction.

The initiator starts the MIMO phase after Beam Refinement Transaction iscompleted. The initiator and the responder can omit the SISO Feedbackprocedure since the SISO Feedback procedure has been completed.

The procedure of FIG. 22 makes it possible for the initiator and theresponder to carry out SISO BFT in combination with SU-MIMO BFT, and toomit the Setup subphase of SISO BRP to reduce the time taken to carryout both SISO BFT and SU-MIMO BFT.

(Modification 2 of Embodiment 3)

Communication apparatuses 100 update the best sector of SISO during MIMOBRP TXSS of FIG. 5. This is called SISO/MIMO BRP TXSS. The SISO trainingcan be omitted and training can be completed early.

FIG. 23 illustrates an example of a procedure for the initiator and theresponder to perform SISO BFT and SU-MIMO BFT. The same BRP frames asthose in FIGS. 4 and 5 are provided with the same reference numerals,and the description thereof is omitted.

The initiator transmits Setup BRP frame 1701.

FIG. 24 illustrates the format of BRP frame 1701. BRP frame 1701includes a TXSS-SISO field and a TXSS-MIMO field. When performing theBFT procedure of FIG. 23, the initiator transmits Setup BRP frame 1701in which the TXSS-SISO field is set to 1 and the TXSS-MIMO field is setto 1. The initiator may also transmit Setup BRP frame 1701 includinginformation on training for reception AWV (e.g., setting the number ofreception AWVs in the L-RX field).

When the responder receives Setup BRP frame 1701, the respondertransmits Setup BRP frame 1702 in which the TXSS-SISO field is set to 1and the TXSS-MIMO field is set to 1.

The initiator and responder transmit EDMG BRP-TX frames 1703 and 1706.While EDMG BRP-TX frames 1703 and 1706 are similar to EDMG BRP-TX frames703 and 706 and EDMG BRP-TX frames 803 and 805, the initiator andresponder perform the same processing as in SISO BFT and the SISO phaseof SU-MIMO BFT when receiving EDMG BRP-TX frames 1706 and 1703. In otherwords, the best sectors necessary for SISO BFT are selected and a listof AWVs necessary for MIMO BFT is kept.

The initiator and responder transmit Feedback BRP frames 1704 and 1707.Each of Feedback BRP frames 1704 and 1707 includes both the informationon the best sector corresponding to the result of SISO BFT (which isincluded e.g., in the BS-FBCK field) and the feedback in the SISO phaseof SU-MIMO BFT (e.g., the values of the EDMG Sector ID Order field andthe SNR field included in the Channel Measurement Feedback element,and/or the EDMG Channel Measurement Feedback element).

The initiator and responder may perform training for the reception AWVsin SISO as in FIG. 4 using EDMG BRP-RX frames 705 and 708.

After completing SISO/MIMO BRP TXSS, the initiator transmits MIMO BFSetup BRP frame 851 a to perform the MIMO phase.

Note that, when the initiator performs SISO BRP TXSS (FIG. 4), theinitiator may use the format illustrated in FIG. 24 for Setup BRP frame701 and transmit the Setup BRP frame in which the TXSS-SISO field is setto 1 and the TXSS-MIMO field is set to 0.

Note that, when the initiator performs MIMO BRP TXSS (FIG. 5), theinitiator may use the format illustrated in FIG. 24 for Setup BRP frame801 and transmit the Setup BRP frame in which the TXSS-SISO field is setto 0 and the TXSS-MIMO field is set to 1.

When the initiator starts the SISO phase of SU-MIMO, the initiatorincludes the TXSS-SISO field and the TXSS-MIMO field in Setup BRP frame1701, sets both the fields to 1, and transmits the Setup BRP frame.

Thus, the initiator and the responder can complete SISO BFT and trainingof the SISO phase of SU-MIMO during the SISO phase of SU-MIMO, so thatit is possible to omit to carry out SISO BRP TXSS to reduce the timetaken to carry out SISO BFT and SU-MIMO BFT.

The present disclosure can be realized by software, hardware, orsoftware in cooperation with hardware. Each functional block used in thedescription of each of the embodiments described above can be realizedby an LSI as an integrated circuit, and each process described in eachof the embodiments may be controlled by the LSI. The LSI may beindividually formed as chips, or one chip may be formed so as to includea part or all of the functional blocks. The LSI may include a data inputand output coupled thereto. The LSI here may be referred to as an IC, asystem LSI, a super LSI, or an ultra LSI depending on a difference inthe degree of integration. However, the technique of implementingintegrated circuits is not limited to LSIs and the integrated circuitsmay be realized by dedicated circuits or general-purpose processors. Inaddition, a Field Programmable Gate Array (FPGA) that can be programmedafter manufacture of the LSI, or a reconfigurable processor in which theconnections and the settings of circuit cells disposed inside the LSIcan be reconfigured may be used.

Note that the present disclosure is intended to be variously modified orvaried by those skilled in the art based on the description presented inthe present specification and known techniques without departing fromthe content and scope of the present disclosure, and such modificationsand applications are encompassed within the scope of the claimedprotection. Further, any combination of features of the above-mentionedembodiments may be made without departing from the content of thepresent disclosure.

A first general aspect of the present disclosure provides acommunication method in which an initiator transmits a first feedbackframe to a responder, the first feedback frame including a BF trainingtype FIELD indicating whether or not beamforming training (BFT) forSingle User Multi-Input Multi-Output (SU-MIMO) is performed aftertransmission sector sweep (TXSS) ends; a responder receives the firstfeedback frame, and transmits second feedback frame to the initiatorwhen the BF training type FIELD indicates that the BFT for SU-MIMO isperformed, the second feedback frame including a Signal to Noise Ratio(SNR) and a sector Identifier (ID) order based on a result of the TXSS;and the initiator receives the second feedback frame, and performs theBFT for SU-MIMO between the initiator and the responder based on the SNRand the sector ID order.

A second general aspect of the present disclosure provides acommunication method for an initiator, the method including:transmitting a feedback frame to a responder, the feedback frameincluding a BF training type FIELD indicating whether or not BFT forSU-MIMO is performed after TXSS ends; and when second feedback frameincluding an SNR and a sector ID order based on a result of the TXSS isreceived from the responder, performing the BFT for SU-MIMO between theinitiator and the responder based on the SNR and the sector ID order.

A third general aspect of the present disclosure provides acommunication method for a responder, the method including: receiving afirst feedback frame from an initiator, the first feedback frameincluding a BF training type FIELD indicating whether or not beamformingtraining (BFT) for Single User Multi-Input Multi-Output (SU-MIMO) isperformed after transmission sector sweep (TXSS) ends; transmittingsecond feedback frame to the initiator when the BF training type FIELDindicates that the BFT for SU-MIMO is performed, the second feedbackframe including a Signal to Noise Ratio (SNR) and a sector Identifier(ID) order based on a result of the TXSS; and performing the BFT forSU-MIMO between the initiator and the responder based on the SNR and thesector ID order.

A fourth general aspect of the present disclosure provides an initiatorcommunication apparatus in which a MAC circuit generates a firstfeedback frame including a BF training type FIELD indicating whether ornot BFT for SU-MIMO is performed after TXSS ends; a transmission circuittransmits the first feedback frame to a responder; a reception circuitreceives second feedback frame from the responder; and when the secondfeedback frame includes an SNR and a sector ID order based on a resultof the TXSS from the responder, the MAC circuit performs BFT with theresponder using the transmission circuit and the reception circuit basedon the SNR and the sector ID order.

A fifth general aspect of the present disclosure provides a respondercommunication apparatus in which a reception circuit receives a firstfeedback frame from an initiator, the first feedback frame including aBF training type FIELD indicating whether or not beamforming training(BFT) for Single User Multi-Input Multi-Output (SU-MIMO) is performedafter transmission sector sweep (TXSS) ends; a MAC circuit generatessecond feedback frame when the BF training type FIELD indicates that theBFT for SU-MIMO is performed, the second feedback frame including aSignal to Noise Ratio (SNR) and a sector Identifier (ID) order based ona result of the TXSS; a transmission circuit transmits the secondfeedback frame to the initiator; and after the transmission circuittransmits the second feedback frame to the initiator, the MAC circuitperforms the BFT for SU-MIMO between the responder and the initiatorusing the transmission circuit and the reception circuit based on theSNR and the sector ID order.

The disclosures of U.S. patent application Ser. No. 62/661,538 filed onApr. 23, 2018 and Japanese Patent Application No. 2019-078100 filed onApr. 16, 2019 including the specifications, drawings and abstracts areincorporated herein by reference in their entirety.

INDUSTRIAL APPLICABILITY

The present disclosure is suitable as a communication apparatusconforming to the 802.11ad standard.

REFERENCE SIGNS LIST

100, 200, 300 Communication apparatus

101 a, 101 b, 201 a, 201 b, 301 a, 301 b Antenna array (transmissionantenna and reception antenna)

102 a, 102 b Switch circuit (SW)

103 a, 103 b Transmission Radio Frequency (RF) circuit

104 a, 104 b Reception RF circuit

109, 109 a RF module circuit

110, 110 a PHY circuit

111 a, 111 b D/A converter

112 a, 112 b A/D converter

113 Array control circuit

114 Coding and modulation circuit

115 Demodulation and decoding circuit

120 MAC circuit

121 Access control circuit

122 Frame generation circuit

123 Frame reception circuit

124 Beamforming (BF) control circuit

130 Host

151, 152 Intermediate Frequency (IF) transfer circuit

153 IF cable

The invention claimed is:
 1. An Initiator apparatus comprising: atransmitter, which, in operation, transmits a feedback request frame toa Responder apparatus after a transmission sector sweep (TXSS), thefeedback request frame including a Beamforming (BF) Training Type fieldin which a value is set, the value being selected from values includinga first value indicating Single Input Single Output (SISO) BF training,a second value indicating single user MIMO (SU-MIMO) BF training, athird value indicating multi user MIMO (MU-MIMO) BF training and afourth value indicating a reserved value; a receiver, which, inoperation, receives a feedback frame from the Responder apparatus, thefeedback frame including a Sector ID Order subfield and a Signal toNoise Ratio (SNR) subfield, wherein the Sector ID Order subfieldindicates a plurality of sector IDs and a plurality of antennascorresponding to at least a portion of sectors used for reception in theTXSS, and wherein the SNR subfield indicates SNRs of the sectors; andcontrol circuitry, which, in operation, performs BF training of a typeindicated by the BF Training Type field, based on the Sector ID Ordersubfield and the SNR subfield.
 2. The Initiator apparatus according toclaim 1, wherein the TXSS is performed by using one of a DirectionalMulti-Gigabit (DMG) Beacon frame, a Sector Sweep (SSW) frame, a ShortSSW frame, and a DMG Beam Refinement Protocol (BRP)-TX frame.
 3. TheInitiator apparatus according to claim 1, wherein the BF Training Typefield is set to 0 to indicate SISO BF training, set to 1 to indicateSU-MIMO BF training, and set to 2 to indicate MU-MIMO BF training. 4.The Initiator apparatus according to claim 1, wherein the feedbackrequest frame includes a TXSS Feedback Request field that indicateswhether a feedback is requested and an SNR Request subfield thatindicates whether an SNR feedback is requested.
 5. The Initiatorapparatus according to claim 4, wherein in response to the feedbackrequest frame including the BF Training Type field set to 0, the TXSSFeedback Request field set to 1, and the SNR Request subfield set to 1,the feedback frame includes a second BF Training Type field set to
 0. 6.The Initiator apparatus according to claim 4, wherein in response to thefeedback request frame including the BF Training Type field set to 1,the TXSS Feedback Request field set to 1, and the SNR Request subfieldset to 1, the feedback frame includes a second BF Training Type fieldset to
 1. 7. The Initiator apparatus according to claim 4, wherein inresponse to the feedback request frame including the BF Training Typefield set to 2, the TXSS Feedback Request field set to 1, and the SNRRequest subfield set to 1, the feedback frame includes a second BFTraining Type field set to
 2. 8. The Initiator apparatus according toclaim 1, wherein both the feedback request frame and the feedback frameare Beam Refinement Protocol (BRP) frames.
 9. A communication method foran Initiator, the communication method comprising: transmitting afeedback request frame to a Responder apparatus after a transmissionsector sweep (TXSS), the feedback request frame including a Beamforming(BF) Training Type field in which a value is set, the value beingselected from values including a first value indicating Single InputSingle Output (SISO) BF training, a second value indicating single userMIMO (SU-MIMO) BF training, a third value indicating multi user MIMO(MU-MIMO) BF training and a fourth value indicating a reserved value;receiving a feedback frame from the Responder apparatus, the feedbackframe including a Sector ID Order subfield and a Signal to Noise Ratio(SNR) subfield, wherein the Sector ID Order subfield indicates aplurality of sector IDs and a plurality of antennas corresponding to atleast a portion of sectors used for reception in the TXSS, and whereinthe SNR subfield indicates SNRs of the sectors; and performing BFtraining of a type indicated by the BF Training Type field, based on theSector ID Order subfield and the SNR subfield.
 10. The communicationmethod according to claim 9, wherein the TXSS is performed by using oneof a Directional Multi-Gigabit (DMG) Beacon frame, a Sector Sweep (SSW)frame, a Short SSW frame, and a DMG Beam Refinement Protocol (BRP)-TXframe.
 11. The communication method according to claim 9, wherein the BFTraining Type field is set to 0 to indicate SISO BF training, set to 1to indicate SU-MIMO BF training, and set to 2 to indicate MU-MIMO BFtraining.
 12. The communication method according to claim 9, wherein thefeedback request frame includes a TXSS Feedback Request field thatindicates whether a feedback is requested and an SNR Request subfieldthat indicates whether an SNR feedback is requested.
 13. Thecommunication method according to claim 12, wherein in response to thefeedback request frame including the BF Training Type field set to 0,the TXSS Feedback Request field set to 1, and the SNR Request subfieldset to 1, the feedback frame includes a second BF Training Type fieldset to
 0. 14. The communication method according to claim 12, wherein inresponse to the feedback request frame including the BF Training Typefield set to 1, the TXSS Feedback Request field set to 1, and the SNRRequest subfield set to 1, the feedback frame includes a second BFTraining Type field set to
 1. 15. The communication method according toclaim 12, wherein in response to the feedback request frame includingthe BF Training Type field set to 2, the TXSS Feedback Request field setto 1, and the SNR Request subfield set to 1, the feedback frame includesa second BF Training Type field set to
 2. 16. The communication methodaccording to claim 9, wherein both the feedback request frame and thefeedback frame are Beam Refinement Protocol (BRP) frames.
 17. TheInitiator apparatus according to claim 1, wherein a BF training typeused in the TXSS and a BF training type indicated by the BF TrainingType field included in the feedback request frame can be different. 18.The Initiator apparatus according to claim 1, wherein the Sector IDOrder subfield indicates the plurality of sector IDs and the pluralityof antennas corresponding to the at least a portion of sectors used forthe reception in the TXSS regardless of which BF training type isindicated by the BF Training Type field included in the feedback requestframe.
 19. The communication method according to claim 9, wherein a BFtraining type used in the TXSS and a BF training type indicated by theBF Training Type field included in the feedback request frame can bedifferent.
 20. The communication method according to claim 9, whereinthe Sector ID Order subfield indicates the plurality of sector IDs andthe plurality of antennas corresponding to the at least a portion ofsectors used for the reception in the TXSS regardless of which BFtraining type is indicated by the BF Training Type field included in thefeedback request frame.